The present invention relates to a method and device for transmission of communications on a bus system, as well as a corresponding bus system.
The networking of control apparatus, sensors, and actuators, with the aid of a communication system or bus system, has drastically increased in the last years in the construction of modern motor vehicles or also in machine construction, in particularly, in the area of machining tools and automation. Synergy effects by separating of function to multiple control apparatus can thereby be achieved. One then speaks in this connection of divided or separated systems. The communication between various stations or participants is to be found more and more via a bus or a bus system. The communication traffic on the bus system, access mechanism, and receiving mechanism as well as error treatment are controlled by means of a protocol.
As protocol in Kfz-region, the CAN (controller area network) is established. This is an event-controlled protocol, that is, protocol activities, such as sending of a message or communication, are initiation by the event, which have their origin externally of the communication system itself. The specific access to the communication system or bus system is enabled via a priority-based bit processing. A supposition is that each message or communication is to be assigned a specific priority. The CAN protocol is very flexible. An addition of further segments and messages is therefore possible without a problem, so long as free priorities are available.
An alternative arrangement to such an event-controlled spontaneous communication is the pure time-controlled application. All communication activities on the bus are strictly periodic. Protocol activities, such as the sending of a communication, are only tripped by means of the progression of a valid time for the entire bus system. The access to the medium is based on the assignment of time ranges or time sections, in which a sender has an exclusive sending right. An addition of new segment is then possible, when previously, the corresponding time section becomes free. This condition forces the communication series already before putting into operation to be established, whereby a schedule is set, which the requirements of repetition rate, redundancy, deadlines, and so forth must satisfy.
Related to the event-controlled application and the pure time-controlled application, a time-controlled CAN application, the so-called TTCAN (time triggered controller area network) is also known. This satisfies the above-described requirements of a time-controlled communication as well as the requirements of a known measure of flexibility. The TTCAN fulfills this through the construction of the communication cycle (basic cycle) in a so-called exclusive window of time or time section for periodic communications of a determined communication participant or substation and in a so-called operating window of time or time section for spontaneous communications of multiple communication substations or participants.
Related to the named bus system is a plurality of bus systems or communications systems for connecting substations or participants in separate systems. In such communication systems, such as, for example, CAN, TTP/C, Bytelight or FlexRay, it is possible to send communications of various lengths. The maximum length of the communication or communication frame, in which these are transmitted, is defined thereby offline as a part of the protocol specification, so that a communication frame can be contained between 0 and n data bytes (n is therefore a protocol-specific constant with nεN0). It is common in all of these protocol that the communication content is secured by means of the addition, in practice, onto the communication content, that is, the communication itself, of a computed security sequence, generally, as binary information, in particular as bits or bytes. That is, the entire communication frame comprises frame parameters, such as, for example, initiation and end bits, the data, and the security sequence. Typically, this security sequence is computed via a security polynomial, in particular, a CRC polynomial (CRC: cyclical redundancy check). This allows bit errors to be detected through the inconsistency between data and CRC bits in a very simple manner. Therefore, it is possible to recognize, with certainty, errors, which are less than a determined amount K (KεN0), that is, contain changed bits. K corresponds therefore with Hamming distance, whereby the value of K is determined by the selection of the security polynomial. With a controller area network, this Hamming distance, for example, can be K=6. With an optimal selection of the Hamming distance, however, the essentially limiting parameters are the maximum communication length as well as the number of supplementary bits. Thus, for example, with 16 supplementary bits and a maximum communication length of 50 data bytes, it is not possible to maintain a Hamming distance of 6, that is, K=6. This is only an example, which shows that a statistically maximum communication length used until now can produced problems in the frame of securing the data transmission.
Thus, as indicated above, the state of the art does not provide optimal results in each respect. Therefore, it is an object of the present invention to resolve the above-described problem and to improve the situation for securing communications, in particular, to achieve a high flexibility.